Typically, lighting is controlled by manual on/off or dimming switches mounted on walls or integral to the lighting fixtures; and heating and air conditioning is controlled by on/off switches and thermostats also integrally or wall mounted. These controls are set by the occupants within a room to the appropriate comfort level. However, when the occupants leave the space, the controls are most often left set to that comfort level. This condition leads to considerable waste of electrical energy through the lighting, heating or air conditioning of the unoccupied space. While it may not be a problem to automatically turn the lights off in the space, it has been customary not to completely turn off the heating and air conditioning within the space because of possible damage to the real estate and possible extreme discomfort to the returning occupants.
Prior art has been applied to the control of lighting equipment by means of various types of occupancy sensors, whereby the lights are automatically turned off when the occupants leave the space. Prior art has also been applied to the heating and air conditioning equipment in the form of timers and computers that automatically schedule the heating and air conditioning on a temporal basis. However, temporal control does not lend itself to irregular or sporadic occupancy of a space as is common in a hotel room or offices. The prior art in occupancy sensors does not lend itself to the application to heating and air conditioning, because it will completely turn the equipment off with the aforementioned consequences.
The present invention improves upon and solves the prior art problems in several ways. Firstly, it improves the occupancy sensor with additional signal processing to extract the occupancy signal in a noisy environment. Secondly, it adds digital timing control that greatly improves settability and stability with aging. Furthermore, the invention combines the lighting function with the control of the heating and air conditioning equipment.
There are several problems that heretofore precluded prior art device application of occupancy sensors to the control of heating and air conditioning equipment that are overcome by the present invention. Firstly, short cycling of electric motors in the equipment was a substantial problem not resolved by prior art. If the motors are frequently turned on and off, their life will be shortened due to heating from inrush current. Prior art occupancy sensors did not include provisions to limit short cycling of the controlled equipment. Secondly, there is the problem of temperature extremes as mentioned above and an adjunct problem of humidity control. If the air conditioning is totally turned off, the space may become too humid and cause real estate damage and excessive discomfort to the occupants upon their return to the space. These prior art problems are solved by the present invention with the addition of circuitry that: Resets the device to the off state when power is lost, which is the reverse of the prior art. The addition of a temperature limit detector, a digital cycle timer and entry delay detector are provided to moderate temperature and humidity fluctuations and limit short cycling, while allowing the lighting function with the control of the heating and air conditioning equipment, thereby enabling the temperature to range above or below the comfort level established by the thermostat settings.